Continuously variable transmission with radial drive

ABSTRACT

A continuously variable transmission in which a circular driver, positioned between and frictionally engaged with op posing surfaces of two oppositely rotatable disks, which are urged towards each other with a biasing mechanism, is mounted to, and is movable axially along, a drive shaft which extends radially from an input shaft which rotates the drive shaft about a longitudinal axis of the input shaft, and wherein output drive is taken from the disks via a speed balancing system.

BACKGROUND OF THE INVENTION

This invention relates to a continuously variable transmission which canbe used in an automotive or other application.

A traction fluid allows a friction drive to be transferred between twosteel interfaces e.g. in a pulley and belt transmission or in a toroidaltransmission. However torque transmission capability and mechanicalefficiency are adversely affected by the following:

-   (1) in a pulley and belt transmission, power is transmitted from a    first pulley via a friction drive to a belt and then from the belt    through another friction drive to a second pulley. In a toroidal    transmission, power is transmitted from a first toroid to a roller    and then from the roller to a second toroid. Thus, in each case,    there are two friction interfaces in series, a configuration which    compounds mechanical losses. For example if the efficiency of each    interface is 90% then the efficiency of two interfaces in series is    81%;-   (2) an input friction radius, and an output friction radius, of a    friction interface vary as a drive ratio varies. For a given input    torque, as the drive ratio changes, this variation requires a    variable clamping force which is typically effected by means of a    hydraulic control system which includes a hydraulic pump the use of    which decreases mechanical efficiency;-   (3) the variation in the input radius, and in the output radius,    limit the torque output, particularly when the input friction radius    is at a minimum. This means that the transmission cannot handle a    maximum value of input torque through its ratio range, and use must    be made of a torque-limiting mechanism which, typically, is    electronically controlled to limit engine power and torque in the    relevant ratios; and-   (4) when an output speed is slightly above zero more torque may be    called for than what the friction drive can supply. If the friction    drive forms a part of a transmission which is installed in a vehicle    it may not be possible for the vehicle to move from a rest position    over a kerb or a similar small obstacle.

GB (1913) 14696 describes a frictional transmission which includes adriver wheel peripherally engaged with planar surfaces of opposed disks.The arrangement is one in which substantial forces are generated, due toan asymmetrical distribution.

GB( 1912) 29132 describes a frictional drive arrangement in which adrive mechanism engages peripherally with two wheels and impartscounter-rotating drive to two disks. An adjustable output drive isprovided by wheels which are axially movable along shafts which arerotated by the disks. The construction is not compact for a substantialvolume exists between the disks. Also, the drive mechanism is loaded bythe disks in one direction and requires components of a substantialstrength to cater for these unidirectional loads.

An object of the present invention is to provide a continuously variabletransmission (CVT) with a radial drive, of compact form, which has abalanced construction which helps to resist loading effects.

SUMMARY OF THE INVENTION

The invention provides a CVT variator which includes a first disk whichis rotatable about a first axis in a first direction and which has afirst disk face, a second disk, spaced from the first disk, which isrotatable about the first axis in a second direction which is oppositeto the first direction and which has a second disk face opposing thefirst face, a drive device which includes a driver with a circular rimand with a central axis, wherein the driver is mounted at a radialdistance from the first axis between the first disk face and the seconddisk face for rotation about the central axis at a first rotationalspeed, a clamping mechanism for urging the disks towards each other sothat the circular rim of the driver is frictionally engaged at a firstcontact location with the first disk face and at a second contactlocation with a second disk face whereby, upon rotation of the driver atthe first rotational speed, the first disk and the second disk arerespectively rotated and produce respective first and second rotationaloutput drives, an actuator for varying said radial distance, and acoupling system which couples together the first and second outputdrives to produce a combined output drive at a second rotational speed.

The coupling system may include a planetary speed balancing system tocompensate for rotational speed differences in the first and secondrotational output drives.

The drive device may include a shaft to which the driver is mounted andwherein the drive is movable along at least a part of a length of theshaft in order to vary said radial distance.

The central axis may be at an angle other than 90° to the first axis.

In one embodiment a surface of the first disk face at the first contactlocation is not parallel to the central axis and a surface of the seconddisk face at the second contact location is not parallel to the centralaxis.

It is possible for the first disk face, and for the second disk face, tobe planar. However in a preferred embodiment the first disk face isconvex and the second disk face is concave.

The variator may include a plurality of said drive devices which, atleast for balancing loads during operation, are preferably equallyangularly spaced apart from one another circumferentially around thefirst axis.

Each central location may, according to design, essentially comprise acontact point i.e. be of minimal dimensions. It is preferred though forthe design to be such that each contact location gives rise to a linecontact i.e. an arrangement in which loading stresses, and hence wear,are reduced.

To cater for a low torque output when the variator is in a low ratio andat a low speed, the variator may be provided in combination with a gearmechanism which transmits power along a power path between an input andoutput and wherein the gear mechanism includes a sprag in the powerpath. the input to the power path constituting, as well, an input to thedrive device and the output from the power path constituting, as well,an output for the combined output drive, whereby the power path is inparallel to a power flow path through the variator, and wherein thesprag is operative to transfer power along the power path from the inputto the output when the ratio of the first rotational speed and the spragis inoperative so as not to transfer power from the input to the outputwhen the variator is at a ratio other than said minimum ratio.

In one form of the invention a circular rim of the driver has a firstsurface which is at an angle less than 90° to the central axis and whichis in contact with the first disk face at the first contact location,and a second surface which is at an angle of less than 90° to thecentral axis and which is in contact with the second disk surface at thesecond contact location.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of examples with reference tothe accompanying drawings in which :

FIGS. 1A and 1B are views in perspective, from first and second sidesrespectively, of a continuously variable transmission (CVT) with aradial drive arrangement, according to the invention, which includes acasing structure, details of which are shown for example in FIGS. 2, 3A,3B, 4A and 4B, and a variator, which is mounted inside the casingstructure, details of which are shown for example in FIG. 6A,

FIG. 2 illustrates in perspective an inner side of a front casing of thecasing structure,

FIGS. 3A and 3B illustrate first and second sides of a middle casing ofthe casing structure,

FIGS. 4A and 4B respectively illustrate a rear casing of the casingstructure from an inner side and an outer side,

FIG. 5A has two views respectively showing a front face and a rear faceof a pressure ring,

FIG. 5B has two views respectively showing a first side and a secondside of a bearing insert,

FIG. 6A, in an upper drawing, shows a variator which, in use, is mountedinside the casing structure shown in FIG. 1, from a first side and in alow ratio configuration, while a lower drawing shows the variator from asecond side and in the low ratio configuration,

FIG. 6B has upper and lower drawings which correspond respectively tothose shown in FIG. 6A but with the variator in a high ratioconfiguration,

FIG. 7 is a plan view of the variator,

FIG. 8 is a perspective exploded view of components of the variator,

FIG. 9 shows the components of FIG. 8 from an opposing side,

FIG. 10A shows in perspective a body of the variator,

FIG. 10B shows in perspective a drive of the variator,

FIG. 11A is a view in cross-section of the variator in a low ratioconfiguration,

FIG. 11B illustrates on an enlarged scale a portion of the variatorwhich is enclosed in a circle marked 11B in FIG. 11A,

FIGS. 12A and 12B illustrate from opposing sides, in perspective, anadjustment device,

FIG. 13 is similar to FIG. 11A but with the variator in a high ratioconfiguration,

FIGS. 14A, 14B and 14C respectively show a front input unit, a rearinput unit and a planetary unit,

FIG. 15A is a perspective view, partly sectioned, of a speed balancingsystem made from the units shown in FIGS. 14A, 14B and 14C,

FIG. 15B shows the speed balancing system in cross-section and from oneside,

FIG. 16A is an end view of a hydraulically actuated piston system,

FIG. 16B shows the piston system of FIG. 16A from one side and incross-section,

FIG. 17 is a block diagram illustrating power flow through differentpaths in the variator,

FIGS. 18A and 18B are different perspective views of an embodiment ofthe variator which addresses a problem of low torque availability at alow variator speed,

FIGS. 19A and 19B are perspective and side views of an alternativeembodiment of the variator,

FIG. 19C illustrates a positioner which is used in the variator of FIGS.19A and 19B,

FIG. 20A is another side view of the variator of FIG. 19A,

FIG. 20B is a cross-sectional view of the variator of FIG. 20A, taken ona line 20B-20B in FIG. 20A,

FIG. 21A is a view in section of a modified variator in a low ratio, and

FIG. 21B shows a different driver.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1A and 1B of the accompanying drawings illustrate, from opposingsides and in perspective, an external configuration of a continuouslyvariable transmission (CVT) 10, with a radial drive arrangement,according to the invention.

The CVT 10 is described hereinafter with reference to its applicationfor use in driving front wheels of a vehicle but this is by way ofexample only and is non-limiting.

The CVT 10 includes a casing structure 12 which is formed from a frontcasing 14, a middle casing 16 and a rear casing 18 (see FIGS. 2, 3 and 4respectively).

A part 20 of an adjustment device 22 (see FIGS. 12A and 12B) protrudesfrom a bearing 76 in the middle casing 16. An end 26 of an input shaft28 (see FIG. 11A protrudes from one side of the front casing 14. A part30 of a direction selector 32 extends from the rear casing 18.

The CVT 10 has a first wheel drive shaft connection 34 and a secondwheel drive shaft connection 36.

The front casing 14, see FIG. 2, has a body 40 on which is mounted afront disk bearing 42, idler bearings 44, a first planetary bearing 46and a first differential bearing 48. An oil seal 50 is positionedadjacent the differential bearing 48.

The body 40 has a peripheral coupling surface 52. The front disk bearing42 is located around a protruding cup 54 through which extends a bore 60centred on a longitudinal axis 62 through which the input shaft 28(FIGS. 1A, 11A) extends. The first differential bearing 48 surrounds abore 66 which coincides with the first wheel drive shaft connection 34(FIG. 1 B).

The middle casing 16 (FIGS. 3A and 3B) includes a body 70, three sets oftwo axially spaced rollers 72 which are spaced by 120° from one anotheron a circumference of a circle extending around the input axis 62, andtwo ratio bearings 76 located in bearing pockets in a protrusion 80 on aside of the body 70. Each roller 72 has a pin 82 which is secured in arespective radial hole 84, and a follower 86 which is rotatably engagedwith the respective pin 82.

A rear disk bearing 88 which is slidable in an axial sense is located ina centre hole 90, of the body 70, which is concentric with the axis 62.

The body 70 has peripheral coupling surfaces 94 and 92 which allow themiddle casing 16 to be securely engaged with the rear casing 18 and thefront casing 14 respectively.

FIGS. 4A and 4B show the rear casing 18 which includes a body 98, asecond differential bearing 100 and an oil seal 102 which are mounted ina cylindrical protrusion 104 on a mating face 106 of the body 98. Asecond planetary bearing 110 and a reverse bearing 112 are located inpockets, not shown, on a recessed surface 114 of a rear mating surface116 of the body 98.

The second differential bearing 100 surrounds a bore 118 inside theprotrusion 104 which is aligned with the second wheel drive shaftconnection 36 (FIG. 1A).

FIGS. 1 to 4 do not illustrate connection structures, bolts and otherfasteners etc. which are used, as is known in the art, to interconnectparts of the casing to one another in a structurally sound and oil tightmanner.

FIG. 5A has two views from opposing sides of a pressure ring 122 whichincludes an annular body 124 and ten compression springs 126 which arepositioned at locations which are equally circumferentially spaced fromone another on a front face 128 of the body 124. In use, free ends 130of the springs 126 bear against a surface 134 of the rear casing 18—seeFIG. 4A.

The annular body 124 includes at a periphery of a rear face 136 aprotruding ring 140 which in use, bears against an outer ring face 142of the rear disk bearing 88 of the middle casing 16—see FIG. 3B.

FIG. 5B has two views of a bearing insert 150 which includes a body 152formed from two substantially circular components 152A and 152Brespectively. A second reverse bearing 154 is centrally mounted to thecomponent 152A and a forward bearing 156 is centrally mounted to thecomponent 152B. The bearings 154 and 156 are flush with a front face 160of the body 152.

In an assembled condition the bearing insert 150 is positioned incomplementary formations 162 and 164 of the middle casing 16 andsimilarly shaped formations 166 and 168 of the rear casing 18.

FIGS. 6A and 6B each have two drawings showing from opposing sides avariator 180 which, in use, is mounted inside the casing structure 12.In FIG. 6A the variator is in a low ratio configuration; in FIG. 6B thevariator is in a high ratio configuration. Attached to the variator, seefor example FIG. 7, is a planetary speed-balancing system 182 details ofwhich are shown in FIGS. 15A and 15B.

FIGS. 8 and 9 are perspective exploded views, from opposing sides, ofcomponents of the variator 180.

The variator 180 includes a front disk 184, a rear disk 186 and a body190.

The front disk 184 has a convex front face 192 formed by an outwardlytapering conical surface. On a rear face 194 the disk 184 has acylindrical protrusion 196 with an outer cylindrical surface 198. At ajunction with the face 194 the protrusion is enclosed by a spur gear200. In use a face 202 of the spur gear 200 bears against a face 204 ofthe front disk bearing 42 included in the front casing 14. The bearing42 functions as a radial, and as an axial, load-carrying bearing.

The rear disk 186 has a conical concave front face 208 formed by aninwardly tapering conical surface. The disk 186, on a rear face 210 isformed similarly to the front disk 184 in that it includes a cylindricalprotrusion 214 with a cylindrical outer surface 216 and a spur gear 218which surrounds a junction of the protrusion 214 and the rear face 210.In use a front face 220 of the spur gear 218 bears against a front face222 of the rear disk bearing 88 in the middle casing 16. The diskbearing 88, in use, provides a radial and an axial load-carryingcapability.

The convex conical angle of the convex front face 192 and the concaveconical angle of the front face 208 may be equal or substantially equal.

The body 190 is generally circular in outline and includes threesubstantially similar segments 230 (see FIGS. 8-10). Each segment 230has a respective generally rectangular cut-out 232 which is flanked by acurved portion 234 of the body. At a radial inner end the cut-out 232has an annular shoulder 236 in which are formed four tapped holes 238.The shoulder 236 surrounds a hole 240 which extends to a central bore242 which is positioned aligned with a central longitudinal axis 246 ofthe body.

At a radial outer side of each rectangular cut-out 232 a respective hole250 extends through a peripheral portion 252 of the body 190.

Each curved portion 234 has, at an outer periphery, a spiralled rib 254which has an outer surface 256 positioned on a radius RS from the axis246. Opposing axial sides of each rib 254 form respective cam surfaces260 and 262.

Axially aligned hollow shafts 264 and 266, which are concentric with thelongitudinal axis 246, extend in opposing directions aligned with theaxis 246. Each shaft 264, 266 carries a respective sleeve 268 and 270 atits outer end.

Two lugs 272 and 274 which are spaced apart in the direction of the axis246, extend radially from one peripheral portion 252 and are positionedadjacent one of the rectangular cut-outs 232. The lugs 272 and 274 haverespective elongate slots 276 and 278.

An input arrangement 280 extends from the shaft 266 (see FIG. 11) whichincludes an input shaft 282 with a bevel gear 284 at one end and splines286 at an opposing end. A shoulder 288 is positioned between the bevelgear 284 and the splines 286.

A small diameter shaft 290 extends to one side of the bevel gear 284.Mounted in the bore 242 are two needle bearings 292, two thrust washers294, a needle thrust bearing 296, an internal circlip 298 and an oilseal 300. The needle bearings 292 are secured in the bore 242 on theoutside and on the inside thereby rotatably locating the input shaft 282which is axially located via the thrust washers 294 and the circlip 298which is engaged with a groove and which secures an outer thrust washer294 to the bore 242. The other thrust washer 294 acts against theshoulder 288.

The input shaft 28 is internally splined at one end so that it canaxially and slidably engage with and drive the splines 286 of the shaft282.

FIG. 10B shows a drive device 310 which includes a bevel drive shaft 312with a bevel gear 322 at one end, a bearing 324 at an opposed end whichis held in position by means of a circlip 326, and an intermediateportion of the shaft which includes splines 328. A driver 330 is locatedbetween the ends of the shaft 312. The driver 330 has a circular body332 with an outer rim 334 which has a radius of curvature CR and a driveradius DR (see FIG. 11B). The body 332 has a splined centre bore 336which is axially and slidably engaged with the splines 328.

A cup assembly 340 is positioned adjacent the bevel gear 322. The cupassembly 340 includes a cap 344 with four countersunk holes (not shown).The cap has a peripheral flat clearance surface 346. Countersunk bolts348, located in the countersunk holes, are in use engaged with thetapped holes 238 so that the cap 344 secures a cap bearing 350 to thebody 190. An inner surface of the cap bearing 350 rotatably positionsthe bevel drive shaft 312 in the body 190. An opposing end of the driveshaft 312 is rotatably secured to the body 190, by engaging an outerside of the bearing 324 with a respective hole 250 in the body 190. Aleading end of the bevel gear 322 bears against the shaft 290 (FIG.11A).

FIGS. 12A and 12B are perspective views from opposing sides of theadjustment device 22 referred to in connection with FIGS. 1A and 1B. Theadjustment device includes a ratio shaft 352 which has a screw thread354 in a central region and a shaft extension 356 at one end. A circlip358 is used to secure one ratio bearing 76 (FIG. 3) to the shaftextension 356. At an opposing end the ratio shaft 352 has a shaftextension 360. A circlip 362 is used to secure the other ratio bearing76 to the shaft extension 360.

An end of the shaft extension 360 forms the part 20 referred to inconnection with FIGS. 1A and 1B.

A lead screw nut 364 and a bracket 366 are engaged with the thread 354.The bracket 366 has a rectangular body 368 with a slotted hole 370, andstuds 392 and 394 at opposing ends. The lead screw nut 364 has acircular body 396 which is centrally threaded to engage with the thread354. A rectangular hook 398 extends from the body 396 and passes overthe rectangular body 368. A washer 400, which abuts an opposing side ofthe body 368 is kept in place by means of a circlip 404. In use thisarrangement prevents the lead screw nut 364 from rotating with thethread 354 together with the ratio shaft 352, while allowing thecircular body 396 to move with a sliding action along the length of theslotted hole 370.

The studs 392 and 394 are respectively engageable with the elongateslots 276 and 278 of the lugs 272 and 274 (FIG. 10A). To facilitateassembly one of the studs 394 and 392 may screw into the rectangularbody 368. The ratio shaft 352 is rotatably secured in the middle casing16 by means of the two ratio bearings 76 and, when rotated, adjusts theposition of the lead screw nut 364 along the thread 354. The position ofthe bracket 366 on the screw thread 354 is simultaneously adjusted andthe body 190 is rotated to some extent around the axis 246 (FIG. 10A)due to the engagement of the studs 394 and 392 with the slots 276 and278.

The ratio shaft 352 may be adjusted in any suitable way, for example bymeans of an automatically or manually controlled electric motor.

The sleeve 270 is rotatably engaged with and is axially slidablerelative to the central bore 60 of the front casing 14. Similarly thesleeve 268 is rotatably engaged with and is axially slidable relative toa central bore 404A on the rear casing 18—see FIG. 4A. The cam surfaces260 and 262 of the ribs 254 are respectively in line contact with thefollowers 86 of the two axially spaced rollers 72 (FIGS. 3A and 3B),with the rib 254 between the rollers 72. When the body 190 is rotatedaround the axis 246 relative to the middle casing 16, the followers 86ride on the cam surfaces of the ribs and, because of the spiral shape ofeach rib 254, the body 190 is axially displaced.

The drivers 330 are between the front disk 184 and the rear disk 186 andare subjected to a clamping force exerted by the compression springs 126on the rear disk 186, via the rear disk bearing 88. The rims 334 of thedrivers 330 are in point contact with the conical convex front face 192of the front disk 184 and in point contact with the conical concavefront face 208 of the rear disk 186 thereby creating a friction drivebetween the drivers 330 and the front and rear disks 184, 186 which arethen rotated in opposite directions. Interfaces of the friction driveinterface are implemented through the use of hardened and polishedsteel-on-steel contact points which operate in a traction fluid similarto that used in commercial belt and pulley, and toroidal, CVTs in theautomotive and allied industries, yielding a coefficient of friction inthe order of 0.1. Alternatively the friction drive interface may beimplemented through the use of steel on friction material contactpoints.

The bevel gears 322 of the drive device 310 mesh with the bevel gear 284of the input arrangement 280 to allow a power source, attached to theinput shaft 28, to drive the input shaft 282. In turn the bevel driveshafts 312 are rotated and impart rotational drive to the drivers 330and, as explained, the front and rear disks 184, 186 are thencounter-rotated.

FIG. 11A shows the drive device 310 with a driver 330 displaced by amaximum extent from the respective bevel gear 322. The driver is inpoint contact with the front disk 184 and the rear disk 186 (radiusRmax=maximum). In this position the variator 180 is in its lowest ratioand the speed of the front disk 184 and of the rear disk 186 is at aminimum. In FIG. 11A the body 190 is shown displaced to the right to amaximum extent.

As the shaft 352 is rotated the body 190 is rotated via the adjustmentdevice 22 and, due to the actions of the followers 86 which are incontact with the cam surfaces 260 and 262, is also moved axially to theleft in FIG. 11. The drivers 330 are forced inwardly to a smallerradius, taken from the axis 246, via the actions of the convex frontface 192 and the concave rear face 208 which respectively present angledsurfaces which are in point contact with the drivers 330.

FIG. 13 shows the drivers 330 at a minimum radius Rmin from the axis246. The body 190 has been moved to the left from the position in FIG.11A by a distance of RM.

Each bevel drive shaft 312 has an axis 398 which is perpendicular to theaxis 246. The convex front face 192 and the concave rear face 208 haveparallel, radially extending contact lines 400B and 402B respectively atan angle 404B relative to the axis 398. A similar situation prevails ifthe front faces 192 and 208 are flat (i.e. not convex nor concaverespectively), parallel to each other and perpendicular to the axis 246.However the axis 398 of the bevel drive shaft 312 must then be at anangle which is not a right angle relative to the axis 246.

In general terms the surfaces 192 and 208 are parallel to each other,but not to the axis 398. This ensures that the body 190 is moved axiallyupon radial movement of the drivers 330.

The radial distance of each driver 330 from the axis 246 can be adjustedwithout any actuator acting directly between the driver 33C) and thesplined shaft 312 on which the drivers are axially slidably located.This is because the convex front face 192 and the concave front face 208are not parallel to the axis 398.

The variator 180 thus functions to generate a drive ratio between theinput shaft 28 and the counter-rotating front and rear disks 184 and 186respectively. The drive ratio can be varied by altering the radialdistance of the drivers 330 from the axis 246.

FIG. 11B shows on an enlarged scale a driver 330 in contact with thefront face 192 of the front disk 184 at a point 406 and in contact withthe front face 208 of the rear disk 186 at a point 408. Due to thecontact radius DR and the angles (inclinations) of the faces 192 and208, the points 406 and 408 are not equally spaced in a radial sensefrom the driver axis 246. Thus the front and rear disks 184 and 186counter-rotate at slightly different speeds. As the radial differencevalue remains the same for different radial positions of the driver 330the difference in the rotational speeds of the front and rear diskschanges with radial movement of the driver 330. Thus the disks 184 and186 cannot be directly coupled together by means of a device with afixed gear ratio. However it might be possible to couple the front disk184 directly to the rear disk 186, if the curvature radius CR issufficiently small so that a small speed difference between therotational speeds of the disks would be acceptable.

FIG. 6A shows the variator 180 in a low ratio configuration i.e. witheach driver 330 at the Rmax position shown in FIG. 11A. FIG. 6B showsthe variator 190 in a high ratio configuration with each driver 330 atthe Rmin position shown in FIG. 13.

The planetary speed balancing system 182 (see FIGS. 14 and 15) is usedto couple outputs of the front and rear disks (184, 186) together in amechanically effective manner to produce a single or combined outputdrive. The speed balancing system 182 includes a front input 412, a rearinput 414 and a planetary unit 416.

The front input 412 engages with an idler gear 418 with an attachmentshaft 420 which is rotatably mounted with the two idler bearings 44 inthe front casing 14 (see upper drawing in FIG. 6A). The input 412includes a front input gear 424 attached to a shaft 428 which at an end430, carries a bevel gear 432. An opposing end 434 of the shaft 428 isrotatably engaged with the first planetary bearing 46 in the frontcasing 14. The end 430 of the shaft 428 is rotatably engaged with thesecond planetary bearing 110 in the rear casing 18. The front input gear424, the idler gear 418 and the spur gear 200 have the same number ofteeth. The idler gear 418 meshes with the spur gear 200 and the frontinput gear 424.

The rear input 414 has a rear input gear 450 which is coupled to a bevelgear 452 via a hollow shaft 454 which has two spaced apart needlebearings 456 in its bore (FIG. 15B). In use the needle bearings 456 runon the shaft 428. The rear input gear 450 has the same number of teethas, and is meshed with, the spur gear 218—see FIG. 6A.

The bevel gear 432 of the front input 412 and the bevel gear 452 of therear input 414 rotate in the same direction with a speed differencebetween the front and rear inputs attributed to the difference betweenthe driving radius of the front disk 184 and the driving radius of therear disk 186, at points 408 and 406 respectively, with each drivingradius measured from the axis 246.

The planetary unit 416 has a cage unit 462, a forward unit 464, areverse unit 470 and a dog sleeve 474.

The cage unit 462 includes a cage 480, a spider bearing arrangement 482and a selector 484—see upper drawing in FIG. 6A. The cage 480 has agenerally cylindrical body 490 with outer splines 492, a centrallypositioned rectangular hole 494 and two holes 496 at a base of therectangular hole 494. The holes 496 are concentric and lie on an axiswhich intersects an axis 500 of the body 490. Bearings 502 respectivelylocated in spaced apart pockets 504 support the cage 480.

The spider bearing arrangement 482 has two bevel spider gears 506. Eachrespective bevel spider gear 506 has a needle bearing 510 in its boreand a needle thrust bearing and washer arrangement 512 at its base. Acentrepiece 514 of the arrangement 482 includes a rectangular body 516with a centrally positioned hole 518 and studs 520 on opposing sides.Each stud is located in a respective hole 496 of the cylindrical body490. The hole 518 is concentric with the shaft 428. The needle bearings510 respectively run on the studs 520. The bevel spider gears 506 canrotate freely around their respective axes in a manner similar to thatwhich exists in an automotive differential unit.

To facilitate assembly at least one of the studs 520 is screwed into thecentrepiece 514.

The bevel gear 432 and the bevel gear 452 have the same number of teethand are meshed with the bevel spider gears 506 to create a planetarygear system.

The forward unit 464 has a forward gear 550 which carries a needlebearing 552 in its centre bore. The forward unit 464 is attached to aforward dog ring 554 which has dog teeth 556 on its rim. The forwardbearing 156 of the bearing insert 150 is secured between the forwardgear 550 and the forward dog ring 554. An inner surface of the needlebearing 552 runs on an outer side of the hollow shaft 454 therebyallowing the forward unit 464 to be axially secured to and to be freelyrotatable around the hollow shaft 454.

Similarly, the reverse unit 470 has a reverse gear 560 with a bearing562 at a central bore. A reverse dog ring 562 on one side has dog teeth564, on its rim, which are identical to the dog teeth 556. An innersurface of the bearing 562 is secured to the shaft 428. The reverse unit470 is thereby axially secured to and is freely rotatable around theshaft 428.

The dog sleeve 474 has a hollow cylindrical body 570 with two spacedapart raised grooves 572 on an outer side and splines 574 on an innerside which mate with the splines 492 of the cage 480. The splines 574also mate with the dog teeth 564 and the dog teeth 556 in such a waythat the dog sleeve 474 is axially slidable around the cylindrical body490.

FIG. 15B shows the dog sleeve 474 in a neutral position at which it isnot engaged with the dog teeth 564 nor with the dog teeth 556.

If the dog sleeve 474 is moved to the left in FIG. 15B it engages withthe dog teeth 556 and couples the forward unit 464 to the cage 480. Ifthe dog sleeve 474 is moved to the right in FIG. 15B it engages with thedog teeth 564 and couples the reverse unit 470 to the cage 480. The dogsleeve 474 is not shown in FIG. 15A in order to clarify theillustration.

Referring to FIG. 6A the selector 484 includes a selector fork 600attached to a selector shaft 602 which is axially and slidably locatedin a hole 606 in the middle casing 16 and in a hole 606B in the rearcasing 18—see FIGS. 3B and 4B. The selector fork 600 is engaged with theraised groove 572 on either side and provides a means for actuating thedog sleeve 474 from a location outside of the casing structure 12 via anextension of the selector shaft 602, referred to as the directionselector 32 in connection with FIG. 1. Such actuation can be manually orautomatically effected.

In operation the front input 412, the rear input 414 and the planetaryunit 416 create the planetary gearing (speed balancing) system 182 withan e-value equal to −1, and with the cage 480 Serving as a planetarygearing cage or arm. This system caters for the difference in therotational speeds of the front input 412 and of the rear input 414. Thusthe rotational speed of the cage 480=(speed of the front input 412+speedof the rear input 414)/2.

The aforementioned expression is for e=−1 but the speed balancing system182 could have an e-value other than −1.

The sizes and teeth numbers of the gears and bevel gears are designed tooptimise operation. The gears may be spur, helical, bevel or spiralbevel gears in order to address performance and cost factors.

FIGS. 6A and 6B illustrate a differential 700B which is coupled to thespeed balancing system 182 and which includes a gear 604 attached, via ahollow shaft 606, to a differential cage 608 which contains spider gears610 and side shaft bevel gears 612 (similar to those found in automotivedrive train differentials), in order to provide drive to left and rightwheels, via suitable splines on the first and second wheel drive shaftconnections 34 and 36 (see FIGS. 1A and 1B).

A front differential end 614 is secured in the first differentialbearing 48 in the front casing 14 (FIG. 2) and a rear differential end616 is secured in the second differential bearing 100 in the rear casing18 (FIGS. 4A and 4B).

The gear 604 meshes with the forward gear 550 to provide forward drivein a vehicle in which the variator is included when the dog sleeve 474is positioned to the left of the position shown in FIG. 15.

A reverse shaft 618 includes a shaft 620 with a gear 622 on one side anda gear 624 on an opposing side. The shaft 620 has a section 626 whichextends beyond the gear 624. The shaft section 626 is rotatably securedin the first reverse bearing 112 in the rear casing 18 (FIG. 4), whilethe shaft 620 is rotatably secured in the second reverse bearing 154 ofthe bearing insert 150 (FIG. 5). The gear 624 and the reverse gear 560of the reverse unit 470 have the same number of teeth and are meshedwith each other. The gear 622 is meshed with the gear 604.

In an operative arrangement the dog sleeve 474 is positioned to theright of the position shown in FIG. 15 so that it engages with the dogteeth 564 and couples the reverse unit 470 to the cage 480. In this wayreverse drive for the vehicle is provided via the reverse shaft 618. Inorder to change the direction of rotation of the gear 604 and so changethe direction in which the vehicle is moving, the front input gear 424and the spur gear 200 can be sized to mesh with each other, the spurgear 218 and the rear input gear 450 can be sized not to mesh with eachother, and the idler gear 418 can be relocated to mesh with the spurgear 218 and with the rear input gear 450.

The variator 180 may be coupled to an internal combustion engine using alaunching device such as a clutch or torque converter. The end 26 of theinput shaft 28 is typically externally splined to engage with internalsplines of a clutch plate.

FIG. 16 shows a hydraulic actuation piston system 640 which isintegrated into the front casing 14 and which is used to actuate amanual transmission clutch. A hollow cylindrical piston 642 is locatedin an axially extending, cylindrical blind groove 644 in the frontcasing 14. The piston 642 carries on a front end a clutch thrust bearing646 and, on a rear end, an external O-ring groove 648 and an internalO-ring groove 650. Each groove 648, 650 carries a respective O-ringthereby to establish a seal between sides of the piston 642 and sides ofthe cylindrical blind groove 644. Hydraulic fluid to the piston system640 is supplied via a channel 652 from a side of the front casing 14 toa base of the cylindrical blind groove 644.

When fluid pressure is applied, via a manually operated pedal orautomatically, the piston 642, via the thrust bearing 646, actuates apressure plate (not shown) of the manual transmission clutch.

FIG. 17 shows a power flow diagram of the variator 180. It is apparentthat each friction interface handles one-sixth of the power which istransmitted. This is a significant benefit in that the power which istransmitted by a friction interface does not pass through a secondfriction interface.

The driver 330 has a driving radius DR (see FIG. 11B) which remainsconstant in all ratios. Therefore for all ratios, a tangential frictionforce at the point of contact with the front disk 184, and with the reardisk 186, remains the same for a given input torque at the input shaft28. Thus the clamping force which is created by the ten compressionsprings 126 is also constant in all ratios. The two tangential frictionforces, produced at the respective points of contact of the driver 330with the front disk 184 and with the rear disk 186, are in oppositedirections with the result that minimal radial forces are exerted on thesplined drive shaft 312 via the driver 330 (FIG. 10B).

The number of segments 230, and thus the number of drive devices 310,may be less than three (as described herein) or more than three.

As previously indicated a problem which could occur with a vehicle, inwhich a CVT is installed, is that at standstill the CVT might not becapable of transmitting sufficient torque to enable the vehicle toovercome an obstacle such as a kerb. The arrangement shown in FIG. 18addresses this problem.

An extension shaft 700 includes a spur gear 702 on one end and abevelled gear, not shown, on an opposing end, which meshes with thethree bevel gears 322 of the drive devices 310 so that the spur gear 702turns at the same speed as the input shaft 28 but in an opposingdirection. The extension shaft 700 is supported by a bearing 704 whichis located in the rear casing 18. The spur gear 702 meshes with a gear706 which, via a sprag 708, drives a gear 710. The gear 710, via asilent chain 712, drives a gear 714 which is attached to the cage 480.

The ratio between the spur gear 702 and the cage 480 (via the gears 706,710 and 714) is the same as the ratio between the spur gear 702 and thecage 480 (via the bevel gears 322, the drivers 330, the front disk 184and the rear disk 186) when the drivers 330 are at the maximum radiusRmax from the axis 246 of the input shaft 28 (FIG. 11A).

The sprag 708 is configured to engage if the speed of the gear 706exceeds the speed of the gear 710 while both are rotating in a directionindicated by an arrow 716. Thus the only situation in which the sprag708 would lock is when the drivers 330 are in the Rmax position and whenmore torque than what the drivers could handle is required. In theabsence of the sprag 708 the drivers 330 would start to slip at theirrespective points of contact with the front disk 184 and the rear disk186—an event which could cause damage to these components. Thus themodified variator is bypassed when the drivers 330 are in the lowestratio, i.e. at a radial displacement of Rmax from the axis 246 of theinput shaft 28.

The preceding explanation is based on the assumption that the inputshaft 28 rotates in the same direction as an engine to which the CVT isattached, i.e. clockwise in FIG. 1A and, in FIG. 18, with the spur gear702 rotating clockwise. In other positions of the drivers 330 the gear706 turns slower than the gear 710 and the sprag 708 freewheels.

The gear 706 is supported, on one side, by a bearing 720 in a modifiedrear casing 18 and on an opposing side by a bearing (not shown) in amodified middle casing 16.

In the modified arrangement shown in FIG. 18 the reverse unit 470 iseliminated. The following changes are made to establish a functionalreverse gear. The dog sleeve 474 is shortened and is attached to a ringgear 724; an idler shaft 726 includes a gear 730 which meshes with thegear 604; an opposing end of the shaft 726 is attached to a gear 736;and bearings 738 and 740 support the idler shaft 726 in a modified rearcasing 18 and in a modified middle casing 16 respectively (not shown).

When the dog sleeve 474 is moved to the right from the position shown inFIG. 18 the ring gear 724 engages with the gear 736 and reverse isestablished. The forward drive function is not altered.

Alternative Embodiment

FIGS. 19 and 20 show a variator 800, modified with reference to what isshown in FIGS. 8 to 10, which includes three identical radialpositioners 802 and a ring gear 804.

The body 190 has a radial hole 806 with its axis parallel to the axis ofeach drive shaft 312. A slot 808 connects the rectangular cut out 232 tothe hole 806. The hole 806 has a bearing pocket 810 close to the axis246 of the input shaft 28 and a bearing pocket 812 displaced from theaxis 246.

Each radial positioner 802 includes a lead screw thread 814 with aneedle bearing 816 on one end and a bearing 818 and a bevel gear 820 onan opposing end.

A lead screw nut 822 has a cylindrical body 826 with a tapped core whichmates with the lead screw thread 814. A rectangular body 828 on one sideof the body 826 carries a stud 830 to which is mounted a roller 834.

For each positioner the cylindrical body 826 is mounted for slidingmovement in a respective radial hole 806 while the rectangular body 828slides in the adjacent slot 808. The roller 834 is in line contact witha radially outer surface of the driver 330. The needle bearing 816 islocated in the bearing pocket 810 and the bearing 818 which is locatedin the bearing pocket 812 is secured in position by means of a circlip840.

The ring gear 804, which is rotatably located in a modified middlecasing 16, is meshed with the three bevel gears 820 and when the ringgear 804 is rotated the bevel gears 820 are rotated. Each lead screw nut822 is moved in a radial direction and the rollers 834 reposition therespective drivers 330, also in a radial direction.

The variator 800 is, as before, used with a front disk 184 and a reardisk 186. If each disk has a respective convex surface then the urgingtogether (by means of the pressure ring 122) of the two convex surfaceson the drivers 330 tends to force the drivers radially outwardly awayfrom the axis 246. The radial outer surfaces of the drivers 330 are thuskept in line contact with the rollers 834.

If the front disk 184 and the rear disk 186 have respective concavesurfaces then the drivers 330 tend to be forced towards the axis 246.The rollers 834 can then respectively be positioned on opposing sides ofthe drivers 330.

If the front disk 184 and the rear disk 186 have respective flatsurfaces then the lead screw nut 822 is modified to have two of thestuds 830, which are radially spaced apart, and two respective rollers834 are used to support each driver 330 on opposing sides.

In the variator 800 a ratio adjustment is done by rotating the ring gear804. During this adjustment the variator 800 does not turn relative tothe middle casing 16. Thus the axially spaced rollers 72 (FIG. 3) andthe ribs 254 (FIGS. 8, 9 and 10) are eliminated. The variator 800 stillmoves axially as needed but is constrained against rotational movementby external structure (not shown). In this configuration the adjustmentdevice 22 is eliminated.

The respective rim of each driver 330 can have any suitable shape tooptimise the friction drive and mechanical efficiency.

If each disk 184, 186 has a concave surface, or a flat surface, or aconvex surface, then there is no radius difference, i.e. the contactpoints 406 and 408 are at the same distance (radius) from the axis 246.The front disk 184 and the rear disk 186 can then be coupled together ina −1 ratio for they rotate at the same speed in different directions.The planetary unit 416 can then be eliminated.

FIGS. 21A and 21B illustrate a modified driver 900 which includes a rim912 with chamfers 904 and 906. The driver 900 is in the same position asthe driver 330 in FIG. 11B. The chamfer 904 in use is in line contact908 with a conical convex front surface 192 of a front disk 184 and thechamfer 906 is in line contact 910 with a conical concave front face 208of a rear disk 186. The line contact configuration, as opposed to apoint contact configuration, reduces contact stresses and allows a morecost-effective material to be used in the drivers and in the disks. Thechamfers 904 and 906 may be suitably shaped and have a slight curvaturein order to optimise traction fluid friction drive and mechanicalefficiency.

Another modification (described with reference to FIG. 18) is to couplean electrical motor, which can serve as a motor or as a generator, tothe extension shaft 700 to produce a hybrid arrangement. In thisconfiguration the wheels of a vehicle in which the variator isinstalled, can be driven via the variator in any of the following modes:

-   engine only (engine clutch engaged and electric motor off);-   engine and motor (engine clutch engaged and electric motor on); and-   motor only (engine clutch disengaged and electric motor on).

The wheels could drive the motor, which then acts as a generator, whenthe vehicle decelerates and the engine clutch is disengaged. The enginecan also drive the motor (acting as a generator) to charge batteries inthe vehicle. In this configuration the dog sleeve 474 is in a neutralposition and the engine clutch is engaged.

If the electric motor is coupled to the cage 480 by a clutch system theengine can charge the batteries via the variator with the engine clutchengaged, and with the electric motor disconnected from the extensionshaft 700.

1. A CVT variator which includes a first disk which is rotatable about afirst axis in a first direction and which has a first disk face, asecond disk, spaced from the first disk which is rotatable about thefirst axis in a second direction which is opposite to the firstdirection and which has a second disk face opposing the first face, adrive device which includes a driver with a circular rim and with acentral axis, wherein the driver is mounted at a radial distance fromthe first axis between the first disk face and the second disk face forrotation about the central axis at a first rotational speed, a clampingmechanism for urging the disks towards each other so that the circularrim of the driver is frictionally engaged at a first contact locationwith the first disk face and at a second contact location with a seconddisk face whereby, upon rotation of the driver at the first rotationalspeed, the first disk and the second disk are respectively rotated andproduce respective first and second rotational output drives, anactuator for varying said radial distance, and a coupling system whichcouples together the first and second output drives to produce acombined output drive at a second rotational speed.
 2. A CVT variatoraccording to claim 1 wherein the coupling system includes a planetaryspeed balancing system to compensate for rotational speed differences inthe first and second rotational output drives.
 3. A CVT variatoraccording to claim 1 wherein the ratio of the first rotational speed tothe second rotational speed is dependent on the size of the radialdistance.
 4. A CVT variator according to claim 1 wherein the drivedevice includes a shaft to which the driver is mounted and wherein thedriver is movable along at least a part of a length of the shaft inorder to vary said radial distance.
 5. A CVT variator according to claim1 wherein the central axis is at an angle other than 90 ⁰ to the firstaxis.
 6. A CVT variator according to claim 1 wherein a surface of thefirst disk face at the first contact location is not parallel to thecentral axis and a surface of the second disk face at the second contactlocation is not parallel to the central axis.
 7. A CVT variatoraccording to claim 1 wherein the first disk face is convex and thesecond disk face is concave.
 8. A CVT variator according to claim 1wherein the first disk face is planar and the second disk face isplanar.
 9. A CVT variator according to claim 1 which includes aplurality of said drive devices, equally angularly spaced apart from oneanother circumferentially around the first axis.
 10. A CVT variatoraccording to claim 1 in combination with a gear mechanism whichtransmits power along a power path between an input and output andwherein the gear mechanism includes a sprag in the power path, the inputto the power path constituting, as well, an input to the drive deviceand the output from the power path constituting, as well, an output forthe combined output drive, whereby the power path is in parallel to apower flow path through the variator, and wherein the sprag is operativeto transfer power along the power path from the input to the output whenthe ratio of the first rotational speed and the sprag is inoperative soas not to transfer power from the input to the output when the variatoris at a ratio other than said minimum ratio.
 11. A CVT variatoraccording to claim 1 wherein a circular rim of the driver has a firstsurface which is at an angle less than 90° to the central axis and whichis in contact with the first disk face at a first contact point formedby the first contact location, and a second surface which is at an angleof less than 90° to the central axis and which is in contact with asecond disk surface at the second contact point formed by the secondcontact location.
 12. A CVT variator according to claim 1 wherein acircular rim of the driver has a first surface which is at an angle lessthan 90° to the central axis and which is in contact with the first diskface at a first contact line formed by the first contact location and asecond surface which is at an angle of less than 90° to the central axisand which is in contact with the second disk surface at a second contactline formed by the second contact location